How to adjust image color space, drawn with builtin shader
With 

shader_code = gpu.shader.code_from_builtin("2D_IMAGE")
print(shader_code["vertex_shader"])
print(shader_code["fragment_shader"])


One can get code for builtin shader and modify it.
Here is mine, just 2 lines changed version:

vertex_shader = '''

    uniform mat4 ModelViewProjectionMatrix;

    in vec2 texCoord;
    in vec2 pos;
    out vec2 texCoord_interp;

    void main()
    {
      gl_Position = ModelViewProjectionMatrix * vec4(pos.xy, 0.0f, 1.0f);
      gl_Position.z = 1.0;
      texCoord_interp = texCoord;
    }

'''
fragment_shader = '''
    in vec2 texCoord_interp;
    out vec4 fragColor;

    uniform float gamma;

    uniform sampler2D image;

    void main()
    {
      fragColor = pow(texture(image, texCoord_interp), vec4(gamma));
    }

'''

shader = gpu.types.GPUShader(vertex_shader, fragment_shader)
shader.uniform_float("gamma", .454)